The present invention relates generally to methods and systems for knockdown and neutralization of toxic clouds of aerosolized chemical or biological warfare (CBW) agents and toxic industrial chemicals using an aqueous decontamination formulation.
Toxic clouds of aerosolized toxic materials can be released by a terrorist attack, or an industrial accident. Methods and systems are needed to rapidly and effectively neutralize the toxic material and render the cloud harmless; thereby saving lives and minimizing impact to infrastructure. Successful knockdown and decontamination of the toxic cloud is a critical goal for both hazmat responders and critical military operations, preferably while the toxic material is still aerosolized.
Toxic clouds can be released in outdoor areas, for example: at industrial sites where accidental chemical spills may occur (train derailment, factories, shipping ports); at open public venues such as outdoor sports stadiums; or indoors (such as subway tunnels or shopping malls). Toxic clouds may also be released from breach of nuclear reactor containment, or during de-militarization of chemical weapons, explosives or other hazardous materials.
Liquid drops of the decontamination fluid falling through a toxic cloud will mechanically scavenge particles and vapors as they fall. The efficiency with which toxic particles and vapors are removed depends on the rate at which material transfers to the drop surface and the rate at which the material is incorporated into the drop. For vapors, Brownian diffusion is the dominant transfer mechanism by which molecules of the material move to the vapor surface. At the drop surface the molecules must be taken into solution to be removed from the gas, which is why it is important to use liquids in which the vapor to be removed is soluble. The dissolved vapor will produce a partial pressure at the drop surface that will retard further mass transfer to the drop surface. As the vapor pressure of the vapor in the gas decreases, it is possible for the dissolved molecules to leave the drop and re-vaporize back into the gas. For this reason, it is necessary for the molecules to be bound or neutralized within the drop liquid reducing the vapor partial pressure at the drop surface.
For particles, the transfer mechanisms are dominated by Brownian diffusion for small particles (<0.1 micrometer), interception for intermediate sized particles (nominally around 1 micrometer) and impaction for large sized particles (>10 micrometer). Electrostatic effects produced by charged drops will enhance collection rates over the range of particle sizes. When the particle contacts the drop surface, it may be collected or bounce off. If the particle is collected, it is helpful if the decontamination fluid wets the particle so that the particle adheres more strongly to the drop, becomes incorporated into the drop, and is removed (scavenged) from the cloud with the drop.
In addition to physically removing (scavenging, knocking-down) aerosolized toxic materials by spraying a decontamination liquid into the toxic cloud, the decontamination spray should also chemically neutralize and/or deactivate the toxic material while the material is still airborne. Also, the decontamination spray should preferably be non-toxic itself, non-corrosive, and water-based.
The “DF-200” family of aqueous decontamination formulations, which are described in more detail in the related patent applications listed above, meets these requirements for being non-toxic and non-corrosive. DF-200 has been shown to be very effective for neutralizing and decontaminating surfaces contaminated by a wide range of chemical or biological warfare agents (e.g., anthrax spores, Yersinia pestis, mustard gas, GD/VX/HD nerve gas agents) and toxic industrial chemicals (e.g., hydrogen cyanide, sodium cyanide, butyl isocyanate, capsaicin, anhydrous ammonia, phosgene, carbon disulfide, malathion).
Against this background, the present invention was developed.